The long-term objective of the proposed research is to learn more about the roles of iron, transferrin, and the transferrin receptor in the processes of lymphocyte activation, and to develop a model to explain the effects of IgG anti-transferrin receptor antibodies (ATRAS) on those processes. Our specific aims are to test the hypotheses that 1) lymphocyte subsets differ in their requirements for uptake of transferrin bound iron for growth, 2) IgG-ATRAS differ in their capacity to reduce transferrin receptor expression and the iron uptake function, and 3) our recently developed IgG ATRA, C2F2, reduces TR expression (and iron uptake function) to a degree such that it produces a unique, highly selective pattern of inhibition of lymphocyte activation protocols. The following methodology will be used in testing our hypotheses. Lymphocyte subsets will be purified by cytotoxic depletion, plate panning, and Percoll gradient banding. Helper and cytotoxic T cell clones will also be employed. 59Fe iron uptake will be measured in serum-free media, and net iron uptake per S phase entry for a given cell type will be derived with the use of flow cytometric cell-cycle analysis and colchicine treatment of lymphocyte cultures. IgG ATRA effects on TR expression will be assessed by flow cytometry. IgG ATRA effects on lymphocte activation protocols will be studied in the MLR, in IL-1 and IL-2-dependent T cell growth assays, and in Con A, PHA, and LPS mitogen induced growth assays. The health relatedness of this proposal derives from the fact of the normal immune response is disturbed under conditions of iron deficiency and iron overload. Major restributions of iron stores in the reticuloendothelial system are characteristic of acute and chronic inflammation and striking alterations of iron metabolism occur in several neoplastic diseases. The proposed studies will contribute to our understanding of these problems.